Chemical Process Calculations: Online Course

A: Option A sounds tempting because fouling is often treated as a thermal issue, but higher metal temperature directly impacts allowable stress under ASME logic. Option C mixes mechanical integrity with thermal qualification; vibration testing doesn’t restore lost stress margin. Option D swaps corrosion allowance for fouling margin, a common cross-domain mistake — corrosion allowance doesn’t address temperature-driven stress reduction. The standard’s intent is pressure boundary safety under worst credible conditions, which fouling changes.

A: A centrifugal unit in A looks familiar, but viscosity kills efficiency and NPSH margin disappears. B handles oxygen sensitivity, yet air drive introduces variability and pulsation that complicates control. D is a real option in lube service, but gear pumps struggle with solids and scale-up fouling risk. The twin-screw in C keeps NPSH low, manages viscosity, and supports inert sealing.

A: A is a common trap — indices don’t override safety intent. B assumes SIL lives only in software, ignoring hardware capability. D imports a system-level assumption without analysis. A SIL mismatch signals a broken safety chain; MOC is needed to realign documents before IQ.

A: B feels intuitive if you picture less heat, but reboiler duty didn’t change. C confuses flooding with reflux reduction. D assumes control loops can violate mass balance. Reduced reflux weakens separation immediately, so top purity slips first.